It is common in the polyester film industry to produce specialty high oxygen and moisture barrier films for use as protective overwrap materials on foods and other oxygen or moisture sensitive products. This can be done with a variety of technologies including, but not limited to coextrusion of barrier polymers such as poly(ethylene vinyl alcohol) “EVOH”, poly(ethylene naphthalate) “PEN” and polyamides, or by subsequent coating of the film using barrier polymers such as EVOH or poly(vinylidene chloride) “PvDC”.
Another common approach to creating a high moisture and oxygen barrier is to overcoat the surface of the film with a layer of metal, such as aluminum or other metals typically using vacuum deposition. The metal layer provides a nearly impenetrable and therefore excellent moisture and oxygen barrier as well as an economical cost for the applications. Representative techniques for depositing nanometer thickness metal onto barrier films are disclosed in such references as U.S. Pat. Nos. 5,631,066 and 6,153,276.
Typically, the process of making metal-overcoated polymer film, i.e., metalized film, generates waste of trim scrap. Trim scrap results from slitting rolls to custom product widths, or from recovered metalized polyethylene terephthalate “PET” film that has defects which cause rejection (e.g., wrinkles, creases, poor metalization). With non-metalized PET, it is industry practice to take trim scrap and defect material and shred it into a flake, pelletize the flake through a secondary extrusion process, crystallize those pellets so that they do not agglomerate during further processing, and use these pellets as part of the resin feed to form a layer, such as a core or skin of a multilayer PET film. That is, the reclaimed material recovered from suitable waste is blended with another component of usually a virgin PET to form the layer of the multilayer PET film.
However, metalized PET has not been recycled. The metal particles can potentially cause web breaks during film formation processing if metalized film reclaim material is fed in a similar manner to non-metalized PET reclaim material. The tendency for web breaks to occur is believed due to the difference in crystallinity Accordingly, trim scrap and defect-containing metalized PET waste has traditionally been discarded at cost of materials, processing cost, and disposal and environmental costs. An objective of this invention is to provide a process that overcomes this difficulty as well as adds benefits of improved properties of the resultant film.